As materials for a support for a photographic material, poly(ethylene terephthalate), triacetyl cellulose, polystyrene, polycarbonate, a laminate of polyolefin laminate and a paper are usually employed due to their excellent transparency. However, such polymer film has a hydrophobic surface, and therefore it is difficult to firmly bond a photographic emulsion layer comprising a hydrophilic polymer (hydrophilic colloid) mainly containing gelatin on the support of the polymer in the case of employing the polymer as the base film of the support for the photographic material.
Two processes can be utilized as a conventional technique which has been tried to overcome the above difficulty:
(1) a process in which after providing a surface activation treatment such as a chemical treatment, a mechanical treatment, a corona discharge treatment, a flame treatment, a UV treatment, a high frequency wave treatment, a glow discharge treatment, an active plasma treatment, a mixed acid treatment and an ozone oxidation treatment, a photographic emulsion layer is directly formed on the support to obtain a high bonding strength; and
(2) a process in which a subbing layer is provided on the support subjected to the above surface treatment by coating, and then a photographic emulsion layer is formed thereon.
The latter process (2) is effective so that it is widely performed.
It is assumed that any of these surface treatments is effected by forming some polar groups on a surface of a base film which is originally hydrophobic and by increasing a cross linking density on a surface, and as a result, it is considered that the affinity of the components contained in a subbing layer with the polar group is increased or the bonding strength between the subbing layer and the base film is enhanced.
Further, various devices are given to the constitution of the subbing layer. There are a multi-layer process in which a layer bonding strongly to a base film (hereinafter referred to as the first subbing layer) is provided as the first layer and a hydrophilic resin layer bonding strongly to a photographic layer is provided thereon as the second layer, and a single layer process in which only a resin layer containing both a hydrophobic group and a hydrophilic group is coated over a base film.
The single layer process, for example, comprising the steps of coating an organic solvent on a poly(ethylene terephthalate) film (which is a representative support for a photographic material) to form a surface having a fine unevenness for the purpose of giving anchoring effect and forming a gelatin layer on the surface. The process is advantageous for obtaining a high bonding strength between a support and a photographic layer (emulsion layer).
However, since the process for the formation of the subbing layer employs the organic solvent, working conditions for performing the process is poor for a worker. Further, there are danger of occurrence of fire and fear of bringing about air pollution. Hence, the process for the formation of the subbing layer using no organic solvent is greatly desired.
As a process for the formation of the subbing layer using no organic solvent (i.e., in water system), for example, there is proposed various processes comprising the steps of coating a polymer latex on a polyester support to form a first subbing layer and forming a hydrophilic colloidal layer comprising gelatin on the first subbing layer. Examples of polymers of the polymer latexes using for the processes include copolymers derived from at least two monomers selected from vinyl chloride, vinylidene chloride, butadiene, methacylic acid, acrylic acid, itaconic acid and maleic anhydride, polyethylene imine, epoxy resin-grafted gelatin, and nitrocellulose.
Particularly, there has been studied the use of a copolymer derived from monomers containing vinylidene chloride or from monomers containing diene (e.g., butadiene) for the first subbing layer in order to enable the formation of the subbing layer in water system by which high bonding strength between the photographic layer and the support of polyester can be obtain.
As a first subbing layer giving the above high bonding strength, the first subbing layer which comprises a copolymer derived from monomers containing diene or combination of the polymer and an appropriate agent for bridge formation (e.g., dichloro-s-triazine) is disclosed (e.g., U.S. Pat. No. 4,542,093, and Japanese Patent Provisional Publications No. 61(1986)-105543 and No. 61(1986)-107343).
However, in the case that after the above subbing layer is provided on a support, a gelatin layer is formed on the subbing layer and a photographic layer and a backing layer are formed on the gelatin layer, the resultant composite (photographic material) is allowed to stand in the condition of a low humidity (10-30% RH), cracking is apt to be produced on the emulsion layer and the backing layer. It is assumed that the photographic layer is shrunk receiving change of humidity owing to a low elastic modulus of the diene-copolymer.
Further, as a first subbing layer giving the above high bonding strength between the support and the photographic layer, a subbing layer which comprises a copolymer derived from monomers containing vinylidene chloride or combination of the polymer and an appropriate agent for bridge formation (e.g., both of dichloro-s-triazine and epoxy compound) is disclosed (e.g., Japanese Patent Provisional Publications No. 1(1989)-180537, No. 1(1989)-209443 and No. 3(1991)-109545).
The photographic material obtained by the use of the above subbing layer does not produce the cracking of the emulsion layer caused by change of humidity around the material. However, in the case that the material is left in the condition of a high humidity for a long time period (e.g., three days), the bonding strength between the support and the first subbing layer is lowered, which results in reduction of the bonding strength between the support and the photographic layer.
Thus, the photographic materials obtained by the use of the above subbing layers do not overcome either the cracking caused by change of humidity around the material or the deduction of bonding strength under the circumstances of a high humidity.
In the photographic material having the first subbing layer and the second subbing layer of gelatin, the photographic emulsion layer is frequently damaged (i.e., suffers from scratch) during a developing operation owing to a foreign matter attached to a roller of the developing machine. Such damage results in formation of pinhole on the emulsion layer after drying the material. Further, in the photographic material having the two subbing layers, when the second subbing layer is formed on the first subbing layer provided on the support, reticulation of the second subbing layer is produced receiving change of humidity. If a coating solution for a photographic emulsion layer or a backing layer is coated at a high coating speed on the second subbing layer having such reticulation, the coated layer exhibits a nonuniform surface. Although the occurrence of the reticulation can be prevented by controlling humidity around the material, a curing rate of the emulsion layer or the backing layer is influenced by a change of humidity.